AUTOMATIC EVALUATION OF INLINE SURFACE TOPOLOGY MEASUREMENT DATA OF MATERIAL JETTED METAL PARTS FOR CLOSED LOOP CONTROL

Additive Manufacturing is becoming increasingly important, which is demonstrated by its rapidly growing market volume. For processing metals, mainly powder based methods such as Powder Bed Fusion (e.g. Selective Laser Melting, Electron Beam Melting) or Direct Energy Deposition (e.g. Laser Metal Deposition) are used. The drawback of these methods is the raw material: Its price per weight is much higher than the raw material price, since powders with a narrow particle size distribution and spherical shape are required for these processes. Furthermore, the handling of the metal powder requires specific safety precautions due to the high risk of fire and negative health implications. Material Jetting is an additive manufacturing method where the build material is deposited onto a platform as single droplets. The raw material can have almost any shape, as it is melted in a crucible. For printing a part, either the build platform or the printhead are moved along a predefined path while droplets are ejected to generate the desired part geometry. For polymers, there are multiple commercially available systems that operate this way. For metal printing however, the systems are still in an early stage of development due to the challenges of the process. Especially generating droplets of a certain size and depositing them at a precise position next to each other is challenging. In this work, a method for a closed-loop layer height control based on inline surface measurement of the printed layers is described. For this, the determined measurement data needs to be automatically processed and compared to the desired layer height. An approach to compensate deviations by individually varying the size of single droplets is described.